Valve for Controlling Gas Exchange, Especially in Internal Combustion Engines

ABSTRACT

A valve for controlling gas exchange, especially in internal combustion engines, comprises, at a valve stem, a stem end and at the other end thereof a valve cone. The valve cone and/or the valve stem are configured as hollow metal elements in such a manner that the hollow elements are entirely or partially filled with a metal foam. The interfaces between the metal and the metal foam are interlinked on the molecular level

This is a continuation of PCT/EP2006/000485, filed Jan. 20, 2006, the contents of which are incorporated herein by reference.

This invention relates to a valve according to the preamble of claim 1. Such valves are preferably used as lightweight valves, as described in German Offenlegungsschrift [Unexamined Application] DE 19804053. Therein the valve cone and valve sealing plug together form a cavity; for weight reasons, the wall thicknesses of these hollow parts are chosen such that they correspond to less than one third of the stem diameter. However, in order to assure sufficient strength, the valve sealing plug in the known lightweight valve is braced against the valve stem inside a radially interior region, and the valve cone is fixed with its upper end to the outside of the stem. This known structural form successfully improves the deformation stiffness of the valve head compared with valves in which a hollow valve stem is made in one piece with the valve cone. In order that all strength requirements can also be satisfied under ignition conditions in the engine, it is necessary in the known lightweight valves to use expensive hardenable materials having high temperature stability.

In contrast, the object of the present invention is to provide lightweight valves of the type mentioned hereinabove, which valves can be manufactured from less expensive material and otherwise satisfy the requirements of high-speed machines, especially internal combustion engines. Because of the danger of high vibrational loads in such high-speed engines, special value is placed on achieving good damping characteristics and at the same time minimizing the wall thickness in order to save weight.

This object is achieved by a valve of the type mentioned hereinabove according to the body of claim 1. By the fact that the valve-forming hollow parts are completely or partly filled with metal foam, a high stiffening effect is achieved, thus making it possible to operate with thin wall thicknesses of the hollow parts forming the valve. To achieve both high strength values and good damping characteristics, it is of substantial importance that the hollow parts forming the valve are bonded metallically at the molecular level over their entire surface with the metal foam.

Options for the metal foam include embodiments both with closed and with open pores. Whereas the closed-pore metal foam offers higher strength, for example when the individual cells have substantially spherical shape, a particular advantage of the open-pore embodiment is that filling with coolant, for example based on sodium, is possible.

In an expedient embodiment, the metal foam has a metal matrix comprising between 5 and 20 vol %, preferably between approximately 8 and 10 vol %. Suitable materials for this purpose are Al, Zn and Fe foams or the like, a metal matrix based on AlSi7 being preferred.

In order to satisfy the requirements of low valve weight, an average density of approximately 0.5 g/cm³ is desirable for the metal foam. In the case of an AlSi7 foam, this would correspond to values of approximately 50 GPa for the modulus of elasticity and 185 MPa for the tensile strength.

As suitable starting material for the metal foam there can be chosen a powder mixture such that a blowing agent will generate a foam volume of approximately five times that of the starting material under the effect of heat.

Advantageously the entire hollow body comprising valve stem and valve head is filled with metal foam. According to an advantageous method for this purpose, it is provided that the starting material for the metal foam is introduced through one open end of the valve stem in such a way that the metal foam completely fills the valve cavity under the effect of heat, and its quantity is adjusted to swell beyond the filling end, after which the excess quantity of metal foam is removed and the filling opening is sealed by welding.

Thus the swelling direction for propagation of the metal foam can be chosen as desired, for example via an opening at the stem end of the valve stem in the direction of the valve head, or by filling the swelling powder through an opening of the valve bottom, for example with the valve sealing plug removed, so that the powder flows toward the closed stem end. After the filling operation, the powder is foamed under the effect of heat, until it swells beyond the existing filling opening in the manner of the method suggested in the foregoing. The temperature is to be selected such that the metal foam becomes permanently bonded to the inside face of the hollow body of the valve.

In order to be able to economize on expensive material, the invention further proposes that the metal envelope forming the valve be welded together from a plurality of portions, which can be made of like or unlike materials.

In an advantageous embodiment, the valve head comprises a valve cone made in one piece with the valve stem as well as a valve sealing plug, joined to one another by electric welding. In this case it can be advantageous for the valve stem to comprise a portion of Nimonic80A at the head end of the valve as well as an end portion of hardenable material surrounding the stem end of the valve, the two portions being joined to one another by friction welding. The end portion, which is to be kept as short as possible, is usually made of X45CrSi93 (DIN 1.4718).

A practical example of the invention is explained hereinafter on the basis of FIG. 1. FIG. 1 shows a longitudinal section through a valve comprising a hollow valve stem 1, a valve cone 2 formed thereon, a valve sealing plug 3 joined to valve cone 2 on the outer circumference by means of a weld 7 made by electric welding, as well as a stem end 4 at the other end of valve stem 1. It is evident that solid stem end 4 is joined by means of a weld 5 to hollow valve stem 1, for which purpose there is used a friction weld. The entire valve cavity is filled with a metal-foam body 6, and the metal foam at its interfaces with the hollow body of the valve forms a molecular bond in the manner of a monolithic structure. 

1. A valve for control of gas exchange, especially in internal combustion engines, comprising a valve cone at one end of a valve stem, the valve stem and/or valve cone being formed as hollow metal parts having a cavity filled at least partly with metal foam to form a metal-foam body, wherein the metal-foam body formed in the valve cavity is bonded metallically at the molecular level at the interfaces with the hollow metal parts forming the valve.
 2. A valve according to claim 1, wherein the metal foam is processed in such a way that it has closed or open pores.
 3. A valve according to claim 1, wherein the metal foam has a metal matrix comprising between 5 and 20 volume percent.
 4. A valve according to claim 3, wherein the metal foam has a metal matrix comprising between 8 and 10 volume percent.
 5. A valve according to claim 1, wherein the metal foam is formed by a metal matrix based on AlSi7.
 6. A valve according to claim 5, wherein the average density of the metal foam is approximately 0.5 g/cm³.
 7. A valve according to claim 5, wherein as starting material for the metal foam there is chosen a powder mixture such that a blowing agent will generate a foam volume of approximately five times that of the starting material under the effect of heat.
 8. A valve according to claim 1, wherein the valve stem and the valve cone are completely filled with metal foam.
 9. A valve according to claim 1, wherein a metal envelope forming the valve is welded together from a plurality of portions, which are made of like or unlike materials.
 10. A valve according to claim 9, wherein a valve head comprises the valve cone made in one piece with the valve stem as well as a valve sealing plug, joined to one another by electric welding.
 11. A valve according to claim 9, wherein the valve stem comprises a portion of Nimonic80A at the head end of the valve as well as an end portion of hardenable material surrounding the stem end of the valve, the two portions being joined to one another by friction welding.
 12. A valve according to claim 11, wherein the end portion is made of X45CrSi93 (DIN 1.4718).
 13. A method for manufacturing a valve according to claim 1, comprising introducing starting material for the metal foam through one open end of the valve stem in such a way that the metal foam completely fills the valve cavity under the effect of heat, and its quantity is adjusted to swell beyond the filling end, after which the excess quantity of metal foam is removed and the filling opening is sealed by welding. 